This application is related to Japanese patent application No. HEI10(1998)-260400 filed on Sep. 14, 1998 whose priority is claimed under 35 USC xc2xa7119, the disclosure of which is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to method for forming a resist pattern, and more particularly to a method for forming a resist pattern having a high dimension controllability in manufacturing a semiconductor device or an integrated circuit.
2. Description of the Related Art
In recent years, miniaturization of patterns is taking place at an accelerated speed in accordance with improvements in integration of semiconductor devices. Naturally, as the miniaturization of the patterns proceeds, a higher dimension controllability of resist patterns is demanded.
Generally, in the case where a resist film applied on a substrate is exposed to light, the light incident into the resist film is repeatedly reflected between a resist film/substrate interface and a resist film/air interface. Due to an interference caused by this multi-reflection of light, a stationary wave is formed in the resist film. In accordance therewith, the amount of light absorbed into the resist film changes periodically in the film. This leads to generation of a distribution in the amount of photolysis of a photosensitive substance and, therefore, to a variation in the dimension of the resist pattern.
Moreover, the intensity of light at a node of the stationary wave changes periodically in accordance with the thickness of the resist film. Therefore, the Eth (the minimum amount of exposure that enables development) of the resist film draws a swing curve that fluctuates with a period of xcex/2n (xcex is an exposure wavelength and n is a refractive index of the resist film) with respect to the thickness of the resist film, as shown in FIG. 6. Therefore, the fluctuation in the thickness of the resist film changes the dimension of the resist pattern.
The thickness of a resist film on an actual device fluctuates locally due to underlayer step differences. Therefore, it is important to reduce the oscillation amplitude of a swing curve (i.e. the stationary wave effect) in view of improving the dimension controllability. Especially, as the exposure wavelength becomes shorter, the reflected light from the underlying substrate becomes stronger, thereby increasing the stationary wave effect. Accordingly, how the oscillation amplitude of the swing curve can be reduced is a problem to be solved in the future.
In order to solve such a problem, the BARC (Bottom Anti-Reflective Coating) method, for example, is proposed. This method is directed to reduction of the effects of multi-reflection in a resist film by reducing the reflectivity at the resist film/substrate interface. Specifically, an antireflection film is formed on a substrate, and a resist is applied thereon.
However, since the antireflection film is located under the resist film in this method, it is necessary to further pattern the antireflection film by means of a developer solution or O2 plasma after a pattern is formed in the resist film. This may lead to increased number of manufacturing steps and to a larger line width shift or variation.
As another method, the TARC (Top Anti-Reflective Coating) method is proposed. This method is directed to reduction of the effects of multi-reflection in a resist film by adjusting the thickness of the antireflection film to allow the phase of the light beam reflected at the resist film/antireflection film interface to be shifted by 180xc2x0 from the phase of the light beam reflected at the antireflection film/air interface so as to cancel these two light beams with each other. Specifically, a water-soluble antireflection film containing PVA (polyvinyl alcohol) as a major component is formed on a resist film, which is then exposed and developed to form a resist pattern.
By this method, the antireflection film may be removed simultaneously in the developing step, so that a required additional step is only the step of applying the antireflection film.
FIG. 5 shows a relationship between the thickness and the Eth of the resist film when an antireflection film is formed on the resist film by means of the TARC method.
From FIG. 5, it will be understood that the value of the stationary wave effect is reduced to about half of the value of the stationary wave effect shown in FIG. 6 where the antireflection film is not used.
However, by this method, the swing curve still has an oscillation amplitude, even though the value of the stationary wave effect may be reduced by 50%.
On the other hand, it is known in the art that, if a transparent film such as SiO2 or SiN is used as an underlayer for the resist film, the amount of light absorbed into the resist film fluctuates with a period of xcex/2n (xcex is an exposure wavelength and n is a refractive index of the underlayer transparent film) in accordance with the variation in the thickness of the underlayer transparent film irrespective of the presence or absence of the antireflection film on the resist film, in the same manner as the case where the thickness of the resist film varies.
FIG. 7 shows a relationship between the thickness of the SiO2 film as the underlayer transparent film and the Eth of the resist film when the thickness of the resist film has, for example, a constant value of 1.05 xcexcm.
From FIG. 7, it will be understood that the period is about 0.12 xcexcm if the exposure wavelength is an i-line beam (0.365 nm) Also, if the thickness of the underlayer transparent film varies by about 0.06 xcexcm corresponding to half of the period, there is a possibility that the stationary wave effect fluctuates to the maximum extent. Therefore, in order to avoid this, the variation in the thickness of the underlayer transparent film must be limited to be less than a thickness that corresponds to half of the period.
However, if an SiO2 film 3 is formed, for example, to a thickness of about 1.0 xcexcm as an interlayer dielectric film on a substrate 1 having a gate electrode 2 of about 0.2 xcexcm thickness formed thereon as shown in FIG. 4, the thickness of the SiO2 film 3 varies by about xc2x10.1 xcexcm. If a contact hole is to be formed simultaneously on the gate electrode 2 and the substrate 1, the thickness difference of the SiO2 film 3 under the resist film 4 is 0.4 xcexcm at the maximum. Therefore, in principle, it is impossible to control the variation of the thickness of the underlayer transparent film to be less than about 0.06 xcexcm.
The present invention has been made in view of these circumstances and the purpose thereof is to reduce the difference between the maximal value and the minimal value of the Eth of the resist film with respect to the variation in the thickness of the underlayer transparent film by controlling the thickness of the resist film and the thickness of the antireflection film, thereby to provide a resist pattern with improved dimension controllability.
Accordingly, the present invention provides a method of forming a resist pattern with a high dimension controllability, comprising the step of: forming an underlayer transparent film on a semiconductor substrate; forming a resist film on the transparent film to a thickness set to be mxc2x7xcex/2n2, where A is an exposure wavelength, n2 is a refractive index of the resist film, and m is an integer from 5 to 30; applying a water-soluble antireflection film on the resist film to a thickness set to be xcex/4n1, where n1 is a refractive index of the antireflection film; and exposing the resist film from above the antireflection film by a beam having a wavelength xcex and developing the resist film as well as removing the antireflection film.
Further, the present invention provides a method for forming a resist pattern with a high dimension controllability, comprising the steps of: forming an underlayer transparent film on a semiconductor substrate; forming a resist film on the transparent film to a thickness set to be (2m+1)xc2x7xcex/4n2, where xcex is an exposure wavelength, n2 is a refractive index of the resist film, and m is an integer from 5 to 30; and exposing by a beam having a wavelength A and developing the resist film.
Also, the present invention provides a substrate capable of forming a resist pattern having a high dimension controllability, the substrate comprising an underlayer transparent film, a resist film, and a water-soluble antireflection film formed successively on a semiconductor substrate, wherein the resist film has a thickness set to be mxc2x7xcex/2n2, where xcex is an exposure wavelength, n2 is a refractive index of the resist film, and m is an integer from 5 to 30; and the water-soluble antireflection film has a thickness set to be xcex/4n1, where n1 is a refractive index of the antireflection film.
Still further, the present invention provides a substrate capable of forming a resist pattern having a high dimension controllability, the substrate comprising an underlayer transparent film and a resist film formed successively on a semiconductor substrate, wherein the resist film has a thickness set to be (2m+1)xc2x7xcex/4n2, where xcex is an exposure wavelength, n2 is a refractive index of the resist film, and m is an integer from 5 to 30.